Generalities
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The sd_gfibre data structure (produced by the defi_geom_fibre command) contains the definition of one or more fiber groups used by the "multi-fiber" elements. This data structure consists of :math:`\mathit{nbgf}` fiber groups.

• Each fiber group is defined by an occurrence of one of the 3 keywords factor section, fiber. and ASSEMBLAGE_FIBRE.

• Each fiber group has a name given by the user.

• Each fiber group contains a certain number of :math:`\mathit{nbfib}` fibers.